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A possible harmony among the planets of the TRAPPIST-1 system

Artist’s illustration of TRAPPIST-1 and its planets (Image NASA/JPL-Caltech)

An article published in the magazine “Astrophysical Journal Letters” describes a research on the orbits of the TRAPPIST-1 system’s planets. NASA’s announcement of the detection of 7 planets in that system of which at least three in the habitable zone raised enthusiasm but the data collected seemed to indicate an instability in those planets’ orbits. A team led by Dan Tamayo of the University of Toronto offers an explanation based on a series of orbital resonances that keep the system stable.

The first analysis of the orbits of TRAPPIST-1 system’s planets caused puzzlement among astronomers because the simulations indicated that they would start destabilizing due to their proximity in less than a million years, very little in astronomical terms. It wasn’t the only reason for prudence about this system’s potential but it seemed to be the main danger to its survival.

The star TRAPPIST-1 is an ultra-cold dwarf that consumes hydrogen so slowly that it might live for trillions of years. It seemed paradoxical that its planets would start crossing each other to end up crashing in such a short time. This would also mean that we were extremely lugky to discover that system.

Now the new research conducted by Dan Tamayo’s team could offer an explanation based on orbital resonance. This is a well-known concept because it was observed in some cases within the solar system but never involving as many planets or moons as are the planets of the TRAPPIST-1 system. In the new simulations of the system, the planets were reproduced starting from their formation and not starting from their current situation, still known with a limited precision.

According to the new simulations, after forming from a protoplanetary disk, TRAPPIST-1’s planets migrated changing their positions following their reciprocal gravitational influences. Over a long time, this phenomenon may have created a harmony among the various orbits, namely the orbital resonance, which resulted in a stability that can last for very long periods even in astronomical terms.

Matt Russo of the Canadian Institute for Theoretical Astrophysics (CITA), where the simulations were conducted, and colleague Andrew Santaguida worked with Dan Tamayo and the Thought Café animation studio to create an animation of the TRAPPIST-1 system. It’s not just a visual reproduction because the harmony of the planets is underlined by musical notes of various instruments.

The result isn’t exactly comparable to a Mozart symphony but the clip at the end of the article gives the idea of ​​what the planets’ possible orbital movements. According to Matt Russo, it’s as if in a group all the members were synchronized to each other almost perfectly, while in general planetary systems are like groups of amateur musicians playing at different speeds.

Unfortunately, observations of the star TRAPPIST-1 carried out with NASA’s Kepler Space Telescope confirm that, despite its really small mass, it’s the source of powerful flares. Its planets are very close to it so they’d need a magnetic field much more powerful than the Earth’s to prevent their atmospheres from being devastated.

This research shows how our knowledge of the TRAPPIST-1 system is still far from exhaustive. It’s been the focus of many scientists for some time so observations and subsequent studies will continue as well as the search for similar systems, stimulated by the confirmation that even tiny stars may have planets.